Metal keys inserted into plastic holders in the standard form of credit cards are known. For this purpose the holder comprises an impression corresponding to the form of the key, which can be completely housed in said impression and be either permanently or releasably connected to it.
Generally if the key is of the releasable type a part of the impression which houses it is shaped in such a manner as to interfere with the head of the key in order to retain it, but to also enable it to be removed. This method is valid in terms of maneuverability of the key when separated from the card, but is less valid from the reliability aspect, as the key can be lost.
If however the key is permanently connected to the card this problem does not arise, but the key is then of poor maneuverability because when turned it also inevitably rotates the card or in any event is hindered by this latter in its movement.